Aaron Brady wrote:
On Dec 20, 8:49 pm, MRAB <goo...@mrabarnett.plus.com> wrote:
Aaron Brady wrote:
On Dec 20, 7:38 pm, Steven D'Aprano <st...@remove-this-
cybersource.com.au> wrote:
Instead of just whinging, how about making a suggestion to fix it? Go on,
sit down for an hour or ten and try to work out how a BINARY OPERATOR
like % (that means it can only take TWO arguments) can deal with an
arbitrary number of arguments, *without* having any special cases.
Go on. Take your time. I'll be waiting.
Hi, not to take sides, but, there is a possibility.
This behavior is currently legal:
"%i %%i" % 0 % 1
'0 1'
So, just extend it. (Unproduced.)
"%i %i" % 0 % 1
'0 1'
"%r %i" % (2, 3, 4) % 1
'(2, 3, 4) 1'
"%r %i" % (2, 3, 4)
'(2, 3, 4) %i'
Which is quite clever and way ahead of its (posessive) time.
A couple of problems:
1. How do you handle a literal '%'? If you just double up then you'll
need to fix the string after all your substitutions.
2. What if a substitution introduces a '%'?
I suppose a possible solution would be to introduce a special format
string, including a literal, eg:
f"%r %i" % (2, 3, 4) % 1
and then convert the result to a true string:
print(str(f"%r %i" % (2, 3, 4) % 1))
(although print() would call __str__ anyway).
The format string would track where the last substitution occurred.
Hmm... I think I'll just learn the new method. :-)
Now that I'm fighting 'r's war for him/her...
Um, here's one possibility. On the first interpolation, flags are
noted and stored apart from subsequent interpolations. Then, use a
sentinel to terminate the interpolation. (Unproduced.)
"%r %i" % ( 2, 3 ) % 0
'(2, 3) 0'
"%% %r" % ( 2, 3 ) % str.interp_end
'% (2, 3)'
"%sss%i" % "%d" % 0
'%dss0'
The first %s is replaced with %d, but doesn't hijack the '0'. If you
want to interpolate the %d, use the sentinel. The sentinel is what
causes '%%' to be handled.
"%sss%i" % "%d" % 0 % 1
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: not all arguments converted during string formatting
"%sss%i" % "%d" % 0 % str.interp_end % 1
'1ss0'
Treating tuples as a special case appears to be the simpler solution,
but this, 'chaining', to adopt the term, is still feasible.
A possible solution occurred to me shortly after I posted, but I decided
that sleep was more important. :-)
The original format is a string. The result of '%' is a string if
there's only 1 placeholder to fill, or a (partial) format object (class
"Format"?) if there's more than one. Similarly, the format object
supports '%'. The result of '%' is a string if there's only 1
placeholder to fill, or a new (partial) format object if there's more
than one.
>>> f = "%r %i"
>>> type(f)
<type 'str'>
>>> f = f % (2, 3, 4)
>>> type(f)
<type 'Format'>
>>> f = f % 1
>>> type(f)
<type 'str'>
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